Although the mainstream light sources for lighting currently are fluorescent lights and incandescent light bulbs, those using LEDs (luminescent diodes) as the light source, compared to fluorescent lights or the like, have less consumption power, longer life span, excellent safety aspects such as not being hot to the touch, and moreover, excellent environmental aspects as they do not contain toxic substances such as mercury, and thus, are anticipated to become the mainstream light sources for lighting in the near future.
White LEDs currently in use are constituted by combining a blue LED and YAG:Ce (yellow emitting phosphor), and bear the problem that they have poor color rendering properties to demonstrate natural color generation ability, such that, particularly when a red-colored object or a person's skin is illuminated with such white LEDs currently in use, colors illuminated by natural light cannot be reproduced. Thus, as a method for improving the color rendering properties of such white LEDs currently in use, constituting a white LED by combining a near-ultraviolet LED and 3 species of emitting phosphors, red, green and blue, or by combining a blue LED and two species of emitting phosphors, red and green, has been examined, and SrGa2S4:Eu has been described as a green emitting phosphor to be used for such purposes (refer to Patent References 1, 2 and 3).
[Patent Reference 1] Japanese Patent Application Laid-open No. 2002-060747
[Patent Reference 2] Japanese Patent Application Laid-open No. 2007-056267
[Patent Reference 3] Japanese Patent Application Laid-open No. 2007-214579
In prior art, green emitting phosphors comprising the described SrGa2S4:Eu, needed to increase luminescent efficiency further. Using an emitting phosphor with a high external quantum efficiency (=internal quantum efficiency×absorption ratio) is important to increase luminescent efficiency. Thus, the present invention focuses on the absorption ratio, which is one of the factors swaying external quantum efficiency, and provides a green emitting phosphor demonstrating excellent absorption ratio so as to increase the luminescent efficiency.